There are work vehicles known in the related art equipped with a cooling fan used to deliver cooling air to a heat exchanger such as a radiator. If the cooling air is supplied along a single flow direction by such a cooling fan, dust that is carried in the cooling air will be delivered to the heat exchanger and will result in clogging. Accordingly, a cooling fan control device that causes the cooling fan to rotate in the reverse direction and thus reverses the air flow direction so as to remove accumulated dirt has been proposed (see patent literature 1).
As an operation is performed to switch the rotation direction of the cooling fan currently rotating forward, the cooling fan control device disclosed in patent literature 1 outputs a control signal for a relief valve, which allows the pressure setting to be adjusted, so as to lower the output-side pressure at the hydraulic pump (the intake-side pressure at a hydraulic motor) to a switch-over pressure, and then after the elapse of a specific length of time that is required to allow the rotation speed at the hydraulic motor to decay, the cooling fan control device outputs a control signal that causes the hydraulic motor to rotate in the opposite direction. Subsequently, it outputs a control signal for the variable relief valve to raise the output-side pressure at the hydraulic pump to a reverse rotation pressure.